The present invention is directed to power supplies for providing operating voltages for line driver devices in communication systems. In particular, the preferred embodiment of the invention is a power supply system for selectively providing operating voltages to line drivers in a telecommunication system.
Line cards are components of digital subscriber line (DSL) chipsets that control operation of line driver devices. A DSL line card preferably uses a chipset which generates a signal to a line driver. The line driver drives a line in a telecommunication system. The chipset and the line driver are preferably physically part of the linecard. Linecards are usually situated in channel banks in a communication system, such as a telecommunication system. Each channel bank typically includes about 70–80 line cards, depending upon the particular implementation. Line cards cooperate with line driver devices to drive the transmission line and load associated with a particular communication loop. Customer provided equipment is coupled at the distal end of a communication loop that is serviced (i.e., driven) by a particular line card among the many line cards in a channel bank. Communication loops may vary significantly in their relevant characteristics. For example, longer lines (i.e., longer loops) and lines that operate at higher data rates require relatively higher power levels at their source. Such long/higher rate lines are known as lossier lines. Shorter lines or lines operating at a relatively lower data rate require a lower power at their source (i.e., lower power at the line card). It is likely that the various loads in a particular communication system will be significantly different among the various communication loops.
Line drivers in communication applications typically use a 15 volt single-ended or split power supply. In practice, the peak-to-peak output voltage from a line driver is limited to a maximum value, typically on the order of 1–2 volts, below the rail-to-rail power supply difference. Power delivered to the line card that is not delivered to the line is dissipated within the line driver as heat.
Heat is generally not desirable in electronic products. In fact, it is the presence of such generated heat that sometimes causes system designers to avoid fully occupying a particular channel bank. If the channel bank is fully populated to its maximum number of line drivers, the heat generated by the fully populated power consumption and the resulting power dissipation could harm the operation of the system and could cause system difficulties.
There are two paramount design considerations observed by designers of line cards and line drivers. One such design consideration is to deliver only the amount of power to a line that is necessary to achieve the desired communications. The other such design consideration is to operate the line driver device under conditions that enable the line driver device to deliver the designed signal to the line while consuming a minimal amount of power.
That is, given the line loss of a receiver (i.e., the sensitivity of the receiver) on the line to be driven, and given the data rate desired for operation of the line, the power to be delivered to the line may be determined. The operating conditions of the line driver may be adjusted for delivering the requisite amount of power to the line with the least distorion attainable. By way of example, and not by way of limitation, specific parameters that are amenable to adjustment in a bipoar transistor amplifier are quiescent current and supply voltage, or voltages. Quiescent current is current passing through an amplifier when no power is being delivered to the load of the amplifier.
The problem of excess power supplied to line drivers and the resultant heat generation by power dissipation is exacerbated by the unpredictability of the load driven by respective line drivers.
There is a need for selective power supply among line drivers in order that appropriate power may be provided to variously loaded line drivers.
There is a need for intelligent provision of selective power supply to line drivers in order to enable communication systems to adapt to various conditions encountered in various communication loops.